For example, a rotation angle detection device for detecting rotation angle of a rotating shaft is conventionally known (refer to, for example, patent document 1). In this rotation angle detection device, a magnet which is formed in disk shape is supported by a rotating shaft, and is maintained to be rotatable in the prescribed direction with the rotating shaft as the center. And, in this rotation angle detection device, two magnetic sensors are provided. The two magnetic sensors consist of hall elements which are arranged so that the line running through the center of the disk and one magnetic sensor and the line running through the center of the disk and another magnetic sensor substantially meet at an angle of 90°. And respective magnetic sensors are arranged below the circumference of the magnet.
Patent document 1: Japanese Patent Application Publication 2003-75108 (from page 2 to 4, FIGS. 4 and 5)